Circuit controlling device for refrigerating systems and the like



Feb. 1, 1955 w 5 BROWN 2,700,878

CIRCUIT CONTROLLI NG DEVICE FOR REFRIGERATING SYSTEMS AND THE LIKE Filed Sept. 27, 1950 2 Sheets-Sheet l Feb. 1, 1955 w 5 BROWN 2,700,878

CIRCUIT CONTROLLING DEVICE FOR REFRIGERATING SYSTEMS AND THE LIKE Filed Sept. 27, 1950 2 Sheets-Sheet 2 a Q I! Hi l- I IH I 1% T Il n l5 ll llllll Ill IIII United States Patent() CIRCUIT CONTROLLING DEVICE FOR REFRIG- ERATING SYSTEMS AND THE LIKE William E. Brown, Pewaukee, Wis., assignor to Cutler- Hammer, Inc., Milwaukee., Wis., a corporation of Delaware Application September 27, 1950, Serial No. 187,107

8 Claims. (Cl. 624) This invention relates to circuit controlling devices, and more particularly to devices adapted for controlling electric refrigerators to afford fully automatic defrosting thereof without danger of food spoilage or thawing of frozen items.

In the prior art appear many forms of fully automatic defrosting devices for electric refrigerators, all of which in general fall into one of two categories, i. e., either they are of the type which effects a defrost period for a fixed period of time without regard to the temperature effected in the refrigerator during such period, or of the type which periodically causes the refrigerator to cycle at a somewhat higher temperature range for a period of time to effect defrosting. In either case the defrost period is ultimately based on a time interval and is not positively responsive to conditions within the refrigerator for termination of the defrost period. Accordingly, defrost periods afforded by prior art devices are calculated to extend over a period of time thought to be sufficient for defrosting the maximum accumulation of frost and result generally in a defrost period of longer duration than necessary. The defrost periods afforded by such devices ultimately depend on calculations which at best must be based on a guess as to average conditions involving a number of variables, such as variations in the rate of ice or frost accumulation, variations in ambient temperature conditions, manufacturing tolerances in the timing device, etc.

The present invention has among its objects the provision of a circuit controlling device affording fully automatic defrosting of electric refrigerators which will initiate a defrost period at predetermined time intervals and which will automatically maintain such defrost period for the shortest period of time necessary to accomplish defrosting of the refrigerator.

More particularly, an object of the invention is to afford a circuit controlling device which will initiate a defrost period chronometrically and positively terminate the same in response to operation of pressure or temperature responsive means.

Another object of the invention is the provision of circuit controlling means for defrosting refrigerators which will initiate a defrost period at predetermined intervals only and will, in response to operation of pressure or temperature responsive means indicative of defrosting temperature in the refrigerator, completely terminate the defrost period thereby cutting off the defrost period automatically within the shortest possible time.

Another object is to provide a circuit controlling device for refrigerators to afford automatic defrosting thereof which will initiate a defrost period chronometrically by opening the motor circuit and positively terminate the defrost period in response to operation of pressure responsive means by closing the circuit without further cycling of the defrost mechanism.

Another object is to provide a circuit controlling device with latching means under the control of chrono- "metric means which will latch such circuit controlling device in a given position and permit movement to un- :'latched position at predetermined time intervals only.

Another object is to provide latching means for circuit controlling devices adapted to afford automatic defrosting of'electric refrigerators, which latching means will afford unlatching of said control device at predetermined intervals to initiate a defrost period and having once unlatched said control device will relatch the same in response to pressure responsive means to terminate the 2,700,878 Patented Feb. 1, 1955 defrost period and will thereafter positively maintain the control device in latched position until time for another defrost period.

Another object is to provide a latching means of the aforementioned character which will positively reset regardless of manufacturing tolerances.

Another object is to provide a latching mechanism of the aforementioned character which is simple and rugged in construction and which may be applied to existing switches.

Another object is to provide a defrosting device for electric refrigerators adapted to be used in conjunction with normal control means to periodically frustrate the latter, but which defrosting device will not of itself cycle, thereby maintaining such period of frustration for a period sufficient only to effect defrosting.

Another object is to provide an automatic defrost mechanism of the aforementioned character which may be added to existing refrigerating systems without alteration thereof and without addition of other devices or parts.

Another object is to provide an automatic defrost mechanism of the aforementioned character which will afford omission of a defrost period under certain conditions.

Another object of the invention is to provide a defrost mechanism of the aforementioned character which may bellmanually set to omit one or more defrost periods at w1 Another object is to provide a combined time setting and cam member for automatic defrost mechanisms of the aforementioned character which may be rotated in either direction without damage to coacting parts and without initiation of unwanted defrost periods.

A still further object is to provide a combined cam and time setting member for mechanisms of the aforemen" tioned character which is simple in construction and affords ease of operation.

Various other objects and advantage of the invention will hereinafter appear.

The accompanying drawings illustrate an embodiment of the invention which will now be described, it being understood that the embodiment illustrated is susceptible of modification without departing from the spirit and scope of the appended claims.

In the drawings,

Figure l is a side elevational view of a control device embodying the invention shown in conjunction with a schematic representation of a typical refrigeration system. The cover of the control device is broken away for purposes of illustration;

Fig. 2 is a top view of the control device illustrated in Fig. 1 with the cover removed;

3 is a sectional view taken on the line 3--3 of 1g.

Fig. 4 is a fragmentary sectional view taken on the line 4-4 of Fig. 3;

Fig. 5 is a developed view of the cam member illustrated in Fig. 3 taken on the line 5-5 thereof; and

Fig. 6 is a fragmentary top plan view of the manually operable means for omitting defrost periods at will shown in side elevation in Fig. 1.

Referring to the drawings, a circuit controlling device designated generally by the reference numeral 10 is shown in Fig. 1 as an automatic defrosting mechanism for a conventional refrigeration system comprising an electric motor M for operating a compressor-condenser a for compressing a volatile refrigerant of well known type. A pipe b connects the high pressure side of the compressor through valve V to the low pressure cooling pipes or evaporator unit 0 in the region which is to be refrigerated. Evaporation takes place and the vapor is drawn through pipe d to the low pressure side of the compressor to complete the cycle.

Motor M is under the control of a switch S of any well known form having a pipe e connecting with pipe d at one end and a metal bellows of the switch at the other end to render switch S responsive to variation in pressure, thereby affording cycling of the motor M in a well known manner to maintain the evaporator within a given temperature range, generally below 32 F.

As will be seen from the drawings, defrosting switch 11) is placed in series relation with the normal control switch S, the circuit being traced from L to the motor M, thence through switch S, to switch 10, and back to L Accordingly, opening of the contacts of switch 10, as will hereinafter be described, will open the circuit to motor M regardless of the position of switch S, thereby for a time frustrating the latter. Thus the defrost switch may temporarily disable switch S to allow the evaporator to rise a predetermined number of degrees above 32 F. to af ford melting and hence removal of the coating of frost which normally builds up thereon.

Defrosting mechanism is designed to initiate such a defrosting period chronometrically at selected times and to positively terminate such defrosting period the first time the evaporator temperature rises a predetermined number of degrees above 32 F., thereby cutting the duration of the defrost period to a minimum. Such operation is accomplished in general through operation of switch 10 to open the motor circuit to initiate the defrost period (thereby disabling switch S as hereinbefore described) and closing the circuit to restore control to switch S to terminate the defrost period.

The circuit controlling device 10 consists in general of a pressure responsive snap action switch means 11, a chronometric device, as for example, a small synchronous motor 12 as illustrated in the drawings, and a latching mechanism for latching the switch means 11, such latching mechanism comprising generally a latching arm 13 (Fig. 3), and a time setting cam member 14 driven by the chronometric device 12 through a suitable gear train (not shown).

The switching means 11 is of the general construction of that illustrated in Kuhn Patent No. 2,158,824 to which reference may be had for the details of construction and operation, it being necessary here to note merely that the switching means 11 includes a pair of stationary contacts 11 to be bridged by a contactor 11 carried by a pivoted insulating member 11. A spring 11 (Fig. l) is attached to member 11 to normally bias contactor 11 into bridging engagement with the stationary contacts 11. A pivoted U-shaped member 11 having a lost motion connection with insulating member 11 carrying contactor 11 is adapted to move the latter to open-circuit position in response to a snap acting mechanism comprising an overcenter spring 11 (Fig. 2) and a pivoted lever 11 the latter being actuated by a pressure or temperature responsive bellows (not shown) of well known form connected to the refrigerating system as heretofore described. It is to be understood that the switching mechanism 11 is so adjusted as to respond to temperatures or pressures in range somewhat above the range of switch S; that is, switch 11 would ordinarily be actuated to open-circuit position at a temperature or pressure above that of the opening point of switch S, and will, of course, be actuated to closed circuit position at a temperature or pressure substantially above that of switch S and above 32 F. to permit defrosting of the refrigerator.

Rigidly attached to one leg of member 11 is a latching arm 13 comprising a relatively thin, resilient intermediate portion 13 and a hook-like portion 13 (Fig. 4) adapted for engagement with cam member 14 as a cam follower.

Cam member 14 is preferably a molded insulating member of circular or disc form having a cylindrical hub portion 14 for attachment to a shaft 15 connected to the chronometric means 12 for rotation of cam 14 in a given direction (clockwise as viewed in Fig. 3). Member 14 is also provided with a knurled rim portion 14 and a ridge 14 formed on one face thereof intermediate said rim and said hub portions and concentric therewith. As best shown in Fig. 4, the innermost side of ridge 14 slopes downwardly to the face of member 14 while the outer edge of ridge 14 is vertical with respect to the face of member 14. The aforementioned vertical side of ridge 14 affords an outer track for cam follower portion 13 of latching arm 13, the latter, under most conditions, being so biased as to tend to hold portion 13' thereof in contact with said outer track, as will hereinafter be described, while the vertical sides of cylindrical hub portion 14 afford an inner track for cam follower 13*. At spaced intervals the ridge 14 is provided with transverse cuts or slots 14 (Figs. 3 and 5) which permit cam follower 13 under its aforementioned bias to transfer, under certain conditions hereinafter to be described,

from the outer track atforded by ridge 14 to the inner track afforded by hub portion 14*. As will hereinafter appear, the transfer of cam follower 13 from the aforementioned outer track to the aforementioned inner track as cam member 14 rotates, affords unlatching of switch mechanism 11 to automatically initiate a defrost period in the refrigerating system, it being understood that one or more of such transverse slots 14 may be provided in ridge 14 and that such slots may be angularly displaced at any interval depending on the number, frequency and time of day at which defrost periods are desired. It is also to be understood that cam member 14 may be rotated by chronometric device 12 at any given speed, the embodiment illustrated in the drawings assuming one complete rotation every 24 hours.

As aforementioned, the inwardly and downwardly sloping innermost side of ridge 14 is also adapted to comet with cam follower 13, the end of which is beveled as best shown at 13 in Fig. 4 to permit cam follower 13 to transfer from the aforementioned inner track to the aforementioned outer track at any point; such transfer occurring under conditions to be hereinafter described during which the bias of latching arm 13 may be reversed, such transfer affording relatching of switch 11 as an incident to termination of the defrost period in a manner hereinafter described.

To facilitate transfer of cam follower 13 from its outer to its inner track, as aforementioned, the face of cam member 14 may additionally be provided with a cam surface 14 (Figs. 3 and 5) adjacent the vertical side of ridge 14 and concentric therewith, such surfaces 14 as may be provided in each case rising from the face of member 14 to a plane substantially half the height of ridge 14, and then leveling off in a plane parallel to the face of member 14, the aforementioned plane of the leveled portion 14 coinciding with the bottom of slots 14 As will be apparent, such cam surfaces 14 as may be provided are in each case positioned so as to precede (with respect to the direction of rotation of cam member 14) and extend across each of the slots 14 provided in ridge 14, and ultimately rejoin or merge with the outer side of ridge 14 at a point beyond each of the slots 14. The cam surfaces 14 are designed to impart a lateral movement to cam follower 13 as it rides upon the top sur face thereof to facilitate transfer of the cam follower from its outer to its inner track, it being understood that the resiliency of the intermediate portion 13 of latching arm 13 permits such lateral movement against an inherent bias of cam follower 13 toward the face of cam member 14.

Moreover, as best shown in Fig. 3, the peripheral side of cam surface 14 (vertical with respect to the face of cam member 14) affords an auxiliary outer track for cam follower 13' which by-passes slot 14 and which track prevents movement of the cam follower through the slot when the cam follower is caused to follow such auxiliary track.

As best shown in Fig. 5, cam surface 14 terminates in a second sloping surface coinciding with one side of slot 14 the latter being of more or less V-shape to prevent binding of cam follower 13 in the slot should a reversal of the bias of arm 13 take place before cam member 14 has been rotated far enough to move slot 14 out of registry with cam follower 13 The reverse face of cam member 14 may be provided with an annular indicating plate or dial 16 (Fig. 1 and Fig. 4) preferably marked in a suitable manner with the hours of the day. As will be understood, when cam member 14 is set in accordance with the hour of the day, the slot or slots 14 afford initiation of a defrost period in accordance with their angular position on cam member 14. To facilitate initial setting or subsequent resetting of cam member 14 as well as to afford external indication of such setting, the cam member 14 is so positioned as to permit its peripheral portion to extend beyond the confines of the enclosing casing of the switch, the cover member thereof, as best shown in Fig. 1, being provided with a slot for such purpose. It will also be observed that the peripheral edge of the rim 14 of member 14 is preferably knurled to facilitate manual setting thereof. Moreover, the provision of the aforementioned auxiliary or by-pass track afforded by portion 14 of cam member 14 permits inadvertent rotation of cam member 14 in a direction the reverse of its normal direction of rotation without damaging cam follower 13 and without permitting it to drop riding onto the auxiliary track and by-passing slot 14 For purposes of describing the mode of operation of the aforedescribed defrost mechanism and its coaction with the refrigerating system in which it is employed, assume that the contacts of defrost mechanism are closed and that the system is under the control of the normal control switch S, which for purposes of illustration may be assumed to open and close the circuit to motor M in such a manner as to maintain the evaporator temperature between a cut-in point of F. and a cut-out point of 10 F. Further assume that the defrosting mechanism 10 if free to operate would open its switch 11 at 26 F. and close the same at 36 F. Under the assumed state of facts the switch 11 would tend to open the motor circuit at all values within the range of control switch S. Accordingly, the latching arm 13 would be biased into engagement with the outer track of cam member 14 afforded by its ridge 14 due to the influence of over-center spring 11 of switch mechanism 11. The aforementioned outer track of cam member 14, however, prevents U-shaped member 11 of switch 11 (rigidly connected to latching arm 13) from actuating contactor carrier 11 in view of the lost motion relationship therebetween, contactor carrier 11 under the bias of spring 11 therefore maintaining its contactor 11 in bridging engagement with stationary contacts 11. Thus the motor circuit (Fig. l) is maintained from L to motor M, through switch S to a terminal T of switch 11, through the contactor 11 to terminal T of switch 11 and thence through a terminal T to L The terminal T is merely a common terminal for L connected both to the T terminal of switch 11 and to chronometric device 12, the latter, as will be apparent, being connected across L L for the supply of electrical energy thereto.

As best shown in Fig. 3, as cam member 14 rotates, cam follower l3 (under its bias as aforedescribed) will travel along the aforementioned outer track to eventually ride up on cam surface 14 and at the appropriate time drop through slot 14, to the inner track afforded by hub portion 14 of cam member 14. Such transfer from outer to inner track permits pivotal movement of arm 13 to unlatch member 11 of switch 11, which in turn strikes the contractor carrier 11 to move the latter against its bias to open the motor circuit regardless of the position of switch S, thereby initiating a defrost period.

When the evaporator has reached a temperature sufficiently high (36 F. under the assumed state of facts) to trip switch 11 to closed position to restore the circuit to motor M, the latching arm 13 will be reset. Such resetting is accomplished through the reversal of the bias of latching arm 13 under the influence of spring 11 to cause the cam follower portion 13 to ride up the inwardly sloping side of ridge 14 and over the edge thereof to restore the cam follower to the outer track, rim portion 14 of the cam member 14 serving as a stop to limit further outward movement of the cam follower.

As will be apparent, as the refrigerating system pulls down to a temperature below the cut-out point of switch 11 (say 26) the latter will again tend to open thus reversing the bias of arm 13 to cause cam follower 13 to catch on the outer track of cam member 14 to prevent such opening of switch 11 until the cam has rotated to a F point where a slot 14 again comes into registry with cam follower 13 Even though the refrigerating system should pull down so quickly as to reverse the bias of arm 13 before cam follower 13 has completely passed out of registry with the slot 14 through which it dropped to initiate a defrost period, the cam follower 13 will not drop a second time through such slot 14 inasmuch as it will be prevented from so doing by the auxiliary or by-pass track 14 afforded by the vertical edge of cam surface 14. Thus switch 11 is positively prevented from cycling the motor and the defrost period is positively terminated by the pressure or temperature responsive means of switch 11, independently of any manufacturing tolerances in the timing mechanism, width of slot 14 or thickness of cam follower 13 etc.

The defrost period, therefore, is of minimum duration thereby effectively preventing food spoilage which might occur where the defrost period is longer than necessary, especially in instances where ambient temperatures are a big factor, as for example, where the refrigerator door is frequently opened, or in reach-in cases which are open at all times.

Moreover, if, as cam follower 13 approaches the cam surface 14 preparatory to initiating a defrost period, the refrigerating system is at an abnormally high temperature, as for example, due to a power failure or an extraordinarily long preceding defrost period, the latching arm and cam follower 13 will be biased toward the rim 14 of cam member 14 and the cam follower will ride on the auxiliary or by-pass track rather than up the cam surface 14. Thus an undesirable defrost period will be automatically skipped.

As best shown in Figs. 1 and 6, the aforedescribed defrost mechanism may additionally be provided with manually operable means affording omission of one or more defrost periods at will. Such manually operable means may comprise a push-button 17 projecting through an opening 18 in the cover member of the mechanism and adapted to engage 11 of the switch 11. Push-button 17 is preferably held in position and biased upwardly out of engagement with member 11 by a resilient metal strip or leaf spring 19 pivotally attached to the cover member as by a rivet 19 The opening 18 (as best shown in Fig. 6) is of more or less key-hole shape affording clearance for push-button 17 at one end thereof, but affording engagement of the cover member with an annular groove 17 for maintaining push-button 17 in depressed position when moved to the dotted line position.

Manual omission of defrost periods may be secured by depressing push-button 17 to move member 11' downwardly and hence cam follower 13 outwardly with respect to cam member 14 to cause the cam follower 13 to remain on the outer track of carn member 14 thus omitting unlatching of switch 11. Such action may be secured if it is desired to omit only one defrost period by momentarily depressing push-button 17 at a time preceding the defrost period to be omitted when the cam follower 13 will be caused to transfer to the auxiliary track 14 of cam member 14, thus causing a slot 14 to be bypassed and the particular defrost period omitted. Or, if it is desired to omit a number of defrost periods, pushbutton 17 may be depressed as aforedescribed and then moved laterally in opening 18 of the cover member to the dotted line position to effect engagement of the cover member edges with the groove 17 to maintain pushbutton 17 depressed, thereby causing cam follower 13 to remain on the outer track of cam member 14 until the push-button is released. Thus defrost periods may be omitted for any period of time at the will of the user.

While the embodiment of the invention just described has been illustrated in connection with pressure responsive switches, it will be obvious that such switches might be operated by temperature responsive thermostats instead of by pressure of the evaporator. It will therefore be understood that the term pressure responsive as used in the appended claims, is meant to include equivalent temperature responsive means. Also it will be clear that the invention may be applied to the control of other forms of energy supply, such as the control of flow of gas by controlling valves, and may be utilized in other ways than as defrosting means in a refrigerating system.

Various modifications of the embodiment of the invention illustrated will readily suggest themselves to those skilled in the art and are intended to be covered if within the scope of the appended claims.

I claim:

1. For an electric switch, in combination,'fluid conditron responsive actuating mechanism for actuating said switch, latching means for maintaining said actuating mechan sm in a given position regardless of the state of said fluid condition, said latching means comprising a latching member connected with said actuating mechanism and having a cam follower portion, a rotatable cam member having first and second tracks for said cam follower and having means including at least one slot affording transfer of said cam follower from said first track to said second track to unlatch said actuating mechanism, and means affording relatching of said actuating mechanism as an incident to operation thereof in response to said fluid condition to actuate said switch by transfer of said cam follower from said second track to said first track at any point thereon, said last mentioned means including an auxiliary track extending across said slot to positively maintain said cam follower in relatched position should such relatching occur while said cam follower and said slot are in registry.

2. For an electric switch, fluid condition responsive actuating mechanism for actuation of said switch, latching means for maintaining said actuating mechanism in a given position regardless of the state of said fluid condition, said latching means comprising a latching arm connected with said actuating mechanism and having a cam follower portion, a rotatable cam member having a first track and a second track for said cam follower and having means including at least one slot affording transfer of said cam follower from said first track to said second track to unlatch said actuating mechanism, said cam being shaped to afford automatic relatching of said actuating mechanism by transfer of said cam follower from said second track to said first track at any point thereon and having an auxiliary track extending across said slot affording a by-pass for said cam follower for preventing unlatching movement thereof for a given state of said condition.

3. For an electric switch, fluid condition responsive actuating mechanism for actuating said switch, latching means for maintaining said actuating mechanism in a given position regardless of the state of said fluid condition, said latching means comprising a latching arm connected to said actuating mechanism and having a cam follower portion, a rotatable cam member having first and second cam surfaces for said cam follower and having means including at least one slot affording transfer of said cam follower from said first cam surface to said a second cam surface to unlatch said actuating mechanism, means aifording automatic relatching in response to the fluid condition of said actuating mechanism by transfer of said cam follower from said second cam surface to said first cam surface at any point on said first cam surface, and manually operable means for relatching said actuating mechanism at will.

4. For an electric switch, fluid condition responsive actuating mechanism for said switch, latching means for maintaining said actuating mechanism in a given position regardless of the state of said fluid condition, said latching means comprising a latching arm connected to said actuating mechanism and having a cam follower portion, a chronometrically driven combined time setting and cam member having a first track and a second track for said cam follower and having means including at least one transverse slot affording transfer of said cam follower from said first track to said second track to afford unlatching of said actuating mechanism at fixed intervals, means affording relatching of said actuating mechanism by transfer of said cam follower from said second track to said first track at any point on the latter as an incident to switch actuating operation of said actuating mechanism in response to said fluid condition, and an auxiliary track extending across said slot affording a bypass for said cam follower to permit setting of said combined time setting and cam member without unlatching said actuating member.

5. For an electric switch, a cam member, a latch having a follower portion for cooperation with said cam member, fluid condition responsive actuating mechanism connected with said latch and movable from one switch actuating position to another, said cam member having a track adapted to maintain said latch in position to prevent movement of said switch actuating mechanism to said one switch actuating position regardless of the state of said condition, said track having a discontinuity at a selected point thereon to release said latch, said cam being formed to permit return of said latch to said track at any point thereon as an incident to movement of said switch actuating mechanism to said other switch actuating position and having an auxiliary track section by-passing said discontinuity and being engageable by said latch when and only when said switch actuating mechanism is moved to said other switch actuating position.

6. For an electric switch, in combination, a cam rotatable at a selected rate, a latch member having a cam follower portion for cooperation with said cam, fluid condition responsive actuating mechanism for said switch connected with said latching member and movable from one switch actuating position to another, said cam afiording a track to retain said latch member in position to prevent operation of said actuating mechanism to said one position regardless of the state of the fluid condition and having a discontinuity to release said latch member and unlatch said actuating mechanism, said cam further having an auxiliary track by-passing said discontinuity and being engageable by said latch member when and only when said actuating mechanism is in said other position.

7. For an electric switch, in combination, snap-acting over-center actuating mechanism movable from a first switch actuating position through an intermediate position on one side of center to a second switch actuating position, a latch connected with said actuating member and having a cam follower portion, a cam member having a track cooperating with said follower portion to latch said actuating member to prevent movement of the same beyond said intermediate position in the direction of said second position, said track having a discontinuity to release said latch and having an auxiliary track section bypassing said discontinuity and engageable by said follower portion as an incident to movement of said actuating mechanism to said first position to relatch said actuating mechanism.

8. A fully automatic defrost mechanism for addition to existing refrigerating systems which includes means to supply energy to the refrigerating system and means for normally controlling said supply of energy, comprising, in combination, switch means for connection in series relationship with said energy supply control means to disable the latter to elfect defrosting of the system and having an actuating mechanism responsive to the temperature in said system to move from one switch actuating position through an intermediate position to another switch actuating position, a latch connected with said switch means, and a movable cam having cam surfaces for cooperation with said latch to latch said actuating mechanism to prevent movement of the same beyond said intermediate position toward said one position and for releasing said latch at a selected time and for relatching said latch as an incident to movement of said actuating mechanism from said other position to said first position to prevent further unlatching of said actuating mechanism, whereby said switch means is permitted to effect but a single disabling action in a selected period regardless of temperature variation in the refrigerating system.

References Cited in the file of this patent UNITED STATES PATENTS 2,095,102 Philipp Oct. 5, 1937 2,114,766 Heitman Apr. 19, 1938 2,162,709 Gill, Sr. June 20, 1939 2,313,390 Newton Mar. 9, 1943 2,410,014 Clark Oct. 29, 1946 2,522,199 Shreve Sept. 12, 1950 2,543,133 Smith Feb. 27, 1951 2,587,026 Beiser Feb. 26, 1952 

